The present invention relates to a new and improved construction of apparatus for the continuous casting of molten metals, especially steel, the molten metal being introduced into a molten metal bath contained within a continuous casting mold by means of a multiplicity of pouring tubes having outlet or discharge openings for the outflowing metal in the form of casting jets, which outlet openings are arranged at a predetermined inclination with respect to the horizontal. The invention also relates to a new and improved method of continuously casting molten metals.
It is already known in this particular field of technology, for the purpose of preventing the formation of non-metallic inclusions in the cast product or strand, to introduce the molten metal, typically steel, flowing out of a tundish by means of pouring tubes into the molten metal bath or liquid metal pool contained within a continuous casting mold. It is conventional practice, especially when casting larger shapes or formats, for instance slabs, to deposit a flux powder upon the surface of the molten metal bath within the continuous casting mold. This flux powder serves to bond the slag particles floating to the surface of the molten bath, thereby preventing incorporation of such slag particles into the continuously cast strand. Different experiments have been carried out and become known which are concerned with the construction of the pouring tubes, their composition and arrangement. Of considerable importance is the angle of the outlet or exit opening, i.e., the direction in which the steel departs from the pouring tube and enters the molten metal bath in the continuous casting mold. If the casting jet flows directly downwardly out of the pouring tube, then the penetration depth of the outflowing steel into the continuous casting mold is considerably greater than if the outflowing casting jet departs laterally from the pouring tube. With increased penetration depth it should be appreciated that the non-metallic inclusions are also transported to a greater downward extent or penetration depth into the liquid core or pool of the cast strand, and thus, when these inclusions tend to rise they can become enclosed in the solidified front or solid-liquid interface of the casting.
In order to overcome such drawbacks the penetration depth therefore must be maintained as small as possible. However, if the deflection of the casting jet is too pronounced following its departure out of the pouring tube, then it is possible for the metal flow to break through or penetrate the protective blanket of the slag or flux layer floating on top of the molten metal bath of the mold and thus come into contact with the atmosphere. When this happens there is present the disadvantageous result that the probability of oxidation and the inclusion of slag particles increases.
A further technique which is part of the state-of-the-art relies upon introducting the steel through more than one pouring tube into the mold. Introduction of the steel into the mold occurs specifically in such a manner that the outlet or discharge openings of the pouring tubes are positioned opposite one another in order to guide the outflowing casting jet streams against one another. However, in this instance there is present the drawback that at the collision or impact zone of the casting jets there occurs a pronounced undesired turbulent flow. Furthermore, the uniformity of the flow of the steel is no longer guaranteed, likewise resulting in an increase in the number of non-metallic inclusions in the cast product. To prevent or minimize the occurrence of such non-uniformity of the steel flow, measures must be provided to insure that the throughflow rate or quantity is continually controlled and regulated. But it is extremely difficult to continuously exactly determine the quantity of throughflowing metal.